ELASTIC BACKSCATTER LIDAR SIGNAL TO NOISE RATIOIMPROVEMENT FOR DAYLIGHT OPERATIONS:POLARIZATION SELECTION AND AUTOMATION

摘要

Signal-to-Noise Ratio (SNR) improvements is one of the important issue in lidarmeasurements, particularly for lidar daytime operations. Skylight background noiseprecincts lidar daytime operations and disturbs the measurement sensitivity. In the past,polarization selective lidar systems have been used mostly for separating and analyzingpolarization of lidar returns for a variety of purposes. A polarization discriminationtechnique was proposed to maximize lidar detected SNR taking advantage of thenatural polarization properties of scattered skylight radiation to track and minimizedetected sky background noise (BGS). In our previous work this tracking techniquewas achieved by rotating, manually, a combination of polarizer and analyzer on boththe lidar transmitter and receiver subsystems, respectively. Minimum BGS take place atpolarization orientation that follows the solar azimuth angle, even for high aerosolloading. In this article, we report a design to automate the polarization discriminationtechnique by real time tracking of the azimuth angle to attain the maximum lidar SNR.Using an appropriate control system, it would then be possible to track the minimumBGS by rotating the detector analyzer and the transmission polarizes simultaneously,achieving the same manually obtained results. Analytical results for New York Cityare summarized and an approach for applying the proposed design globally isinvestigated.